1. Field of the Invention
The present invention relates to a safe opening container lid and a process for producing the same. More particularly, the present invention pertains to a container lid which may be applied to various kinds of containers opened with a tear tab and which is designed so that, after the container is opened, safe open edges remain on both the curled, or bead, portion of the lid and the removable plate portion torn off from the lid body. The present invention also relates to a process for producing the safe opening container lid described above.
2. Description of the Related Art
There are a great variety of containers for foods and soft drinks which are designed to be opened by tearing the container lid along a tear line formed therein using a tear tab.
Container lids for these containers have the following problems. After the container has been opened, the sharp edges remaining on both the torn-off removable plate portion and the bead side plate portion that is curled with respect to the container body may injure the user's skin when he or she takes out the contents or eats or drinks the food or soft drink directly from the container, and the removable plate portion torn off from the lid body is extremely dangerous if it is thrown away carelessly. In general, an aluminum or aluminum alloy sheet or a surface-treated steel sheet of tin or tin-free steel is employed as a lid material. Among container lids made of these materials, those made of the latter material are said to be particularly dangerous.
Therefore, various attempts have heretofore been made to leave the above-described open edges as safe as possible (see Japanese Utility Model Publication No. 58-40032/1983, Japanese Patent Application Nos. 60993/1984 and 198569/1985, etc.).
For example, the container lid disclosed in Japanese Patent Application No. 60993/1984 is arranged as shown in FIG. 10 which is a sectional view of an essential part thereof. More specifically, a loop portion 102 is formed at the outer side of a tear line 101 such that the return portion 103 of the loop portion 102 which returns toward the tear line 101 projects inward slightly beyond the tear line 101 (the amount of projection: Z1), and a tear tab 104 is fitted to a removable plate portion 105 such that the tip of the tab 104 is disposed at the tear line 101. According to this container lid, when the removable plate portion 105 is torn off along the tear line 101 using the tear tab 104, the open edge (101) remaining on the annular inclined portion 106 continuing from the bead is located at the outer side of the return portion 103. Therefore, even after the container lid is fully opened, the peripheral edge is safe and presents no hazard to the user.
FIG. 11 shows an essential part of the container lid disclosed in Japanese Patent No. 62-64729. In this prior art, the lid stock is bent to form a raised wall 108 around the peripheral edge of a removable plate portion 107 such that the outer peripheral rising portion is above the inner peripheral rising portion (the level difference: Z2). A tear line 109 is formed in the outer peripheral rising portion, and a tear tab 110 is fitted to the removable plate portion 107 such that the tip of the tab 110 is disposed at the tear line 109. According to this container lid, when the removable plate portion 107 is torn off along the tear line 109 using the tear tab 110, the sharp edge remains in close contact with the area of the raised wall 108 that is between the bent portion and the inner rising portion, thus enabling the open edge to be present in safe form.
Japanese Utility Model Publication No. 40032/1983 also discloses a technique of leaving the open edge on the bead side plate portion or the removable plate portion in safe form.
The above-described inventions are arranged so that the open edge remaining on the bead side plate portion or the removable plate portion is present in safe form. These prior arts are, however, incapable of forming safe open edges on both the bead side plate portion and the removable plate portion.
Container lids of the type described above may also be applied to containers for storing combustible liquids or the like. It has recently been provided by the fire laws that containers for storing combustible liquids should undergo a drop test and should have sufficient strength to withstand the drop impact. If the container lid is torn open along the tear line when the container drops, the container would fail to pass the drop test. The same is the case with containers for ordinary soft drinks. In any case, the tear portions of container lids must have a structure which satisfactorily withstands the impacting internal pressure generated when the container drops.
In regard to problems experienced in the manufacture of container lids, container lids which have been formed are sprayed with a maintenance varnish to coat the surfaces for the purpose of rust prevention, and the portion that is provided with a tear line is particularly required to be completely coated with the maintenance varnish. Even when a loop portion or a bent raised wall is formed to provide a safe open edge as described above, if the tear line is not satisfactorily coated with the maintenance varnish, the container lid cannot be applied to containers for beverages or foods.